Bearing device for a wheel

ABSTRACT

A bearing device includes a recess-projection fitting structure in which a hub wheel and a shaft section, which is fitted in a hole of the hub wheel of the outer joint member of the constant velocity universal joint, are unitized together. In the recess-projection fitting structure, entire fitting regions among projections on the outer surface of the shaft section of the outer joint member and recesses, which fit on the projections, are brought into intimate contact with each other.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional application of U.S. application Ser.No. 12/530,834, now U.S. Pat. No. 8,757,887, issued Jun. 24, 2014, whichis a U.S. National Stage Application of International (PCT) ApplicationNo. PCT/JP2008/054660, filed on Mar. 13, 2008.

TECHNICAL FIELD

The present invention relates to a bearing device for a wheel forsupporting wheels to freely rotate relative to a vehicle body in avehicle such as an automobile.

BACKGROUND ART

The bearing device for a wheel has evolved from a structure called firstgeneration in which roller bearings in double rows are independentlyused to second generation in which a vehicle body attachment flange isintegrally provided in an outer member. Further, third generation inwhich one inner raceway surface of the roller bearings in double rows isintegrally formed with an outer circumference of a hub wheel integrallyhaving a wheel attachment flange has been developed. Further, fourthgeneration in which a constant velocity universal joint is integratedwith the hub wheel and the other inner raceway surface of the rollerbearings in double rows is integrally formed with an outer circumferenceof an outer joint member constituting the constant velocity universaljoint has been developed.

For example, the bearing device for a wheel called third generation isdescribed in Patent Document 1. The bearing device for a wheel calledthird generation includes, as illustrated in FIG. 22, a hub wheel 102having a flange 101 extending in an outer diameter direction, a constantvelocity universal joint 104 having an outer joint member 103 fixed tothis hub wheel 102, and a roller bearing having an outer member 105arranged on an outer circumferential side of the hub wheel 102.

The constant velocity universal joint 104 includes the outer jointmember 103, an inner joint member 108 arranged in a cup-shaped section107 of this outer joint member 103, a ball 109 arranged between thisinner joint member 108 and the outer joint member 103, and a cage 110that retains this ball 109. A spline section 111 is formed on an innercircumferential surface of a center hole of the inner joint member 108.An end spline section of a shaft (not shown) is inserted into thiscenter hole, whereby the spline section 111 on the inner joint member108 side and the spline section on the shaft side are engaged.

Further, the hub wheel 102 includes a cylinder section 113 and theflange 101. A short-cylindrical pilot section 115, on which a wheel anda brake rotor (not shown) are mounted, is protrudingly provided on anouter end surface 114 (end surface on an opposite joint side) of theflange 101. Note that, the pilot section 115 includes a large-diameterfirst section 115 a and a small-diameter second section 115 b. The brakerotor is externally fitted onto the first section 115 a, and the wheelis externally fitted onto the second section 115 b.

Then, a notch section 116 is provided in an outer circumferentialsurface at an end portion on the cup-shaped section 107 side of thecylinder section 113. An inner race 117 is fitted in this notch section116. A first inner raceway surface 118 is provided near a flange on anouter circumferential surface of the cylinder section 113 of the hubwheel 102. A second inner raceway surface 119 is provided on an outercircumferential surface of the inner race 117. Further, a bolt insertinghole 112 is provided in the flange 101 of the hub wheel 102. A hub boltfor fixing the wheel and the brake rotor to this flange 101 is insertedinto this bolt inserting hole 112.

In the outer member 105 of the roller bearing, double-row outer racewaysurfaces 120, 121 are provided on an inner circumference thereof, and aflange (vehicle body attachment flange) 132 is provided on an outercircumference thereof. A first outer raceway surface 120 of the outermember 105 and the first inner raceway surface 118 of the hub wheel 102are opposed to each other. A second outer raceway surface 121 of theouter member 105 and the raceway surface 119 of the inner race 117 areopposed to each other. Rolling elements 122 are interposed between thoseinner and outer raceway surfaces. That is, an inner member of the rollerbearing is constituted by the inner race 117 and a part of the outersurface of the hub wheel 102.

A shaft section 123 of the outer joint member 103 is inserted into thecylinder section 113 of the hub wheel 102. In the shaft section 123, ascrew section 124 is formed at an end of a reverse cup-shaped sectionthereof. A spline section 125 is formed between this screw section 124and the cup-shaped section 107. Further, a spline section 126 is formedin an inner circumferential surface (inner surface) of the cylindersection 113 of the hub wheel 102. When this shaft section 123 isinserted into the cylinder section 113 of the hub wheel 102, the splinesection 125 on the shaft section 123 side and the spline section 126 onthe hub wheel 102 side are engaged.

A nut member 127 is screwed onto the screw section 124 of the shaftsection 123 projecting from the cylinder section 113. The hub wheel 102and the outer joint member 103 are connected. An inner end surface (rearsurface) 128 of the nut member 127 and an outer end surface 129 of thecylinder section 113 come into contact with each other and an endsurface 130 on the shaft section side of the cup-shaped section 107 andan outer end surface 131 of the inner race 117 come into contact witheach other. In other words, when the nut member 127 is tightened, thehub wheel 102 is nipped by the nut member 127 and the cup-shaped section107 through an intermediation of the inner race 117.

CITATION LIST Patent Literature

[Patent Document 1] JP 2004-340311 A

SUMMARY OF INVENTION Technical Problem

Conventionally, as described above, the spline section 125 on the shaftsection 123 side and the spline section 126 on the hub wheel 102 sideare engaged. Therefore, it is necessary to apply spline machining toboth the shaft section 123 side and the hub wheel 102 side, and hencecost increases. When the shaft section 123 is press-fitted into the hubwheel 102, recesses and projections of the spline section 125 on theshaft section 123 side and the spline section 126 on the hub wheel 102side need to be aligned. In this case, if the shaft section 123 ispress-fitted into the hub wheel 102 by aligning tooth surfaces thereof,recessed and projected teeth are likely to be damaged (torn). Further,if the shaft section 123 is press-fitted into the hub wheel 102 byaligning the spline sections to a large diameter of the recessed andprojected teeth rather than aligning the tooth surfaces, a backlash in acircumferential direction tends to occur. As described above, if thereis the backlash in the circumferential direction in this way,transferability of rotation torque is low and noise tends to occur.Therefore, when the shaft section 123 is press-fitted into the hub wheel102 by the spline fitting as in the prior art, it is difficult to solveboth the damages to the recessed and projected teeth and the backlash inthe circumferential direction.

Further, it is necessary for the nut member 127 to be screwed on thescrew section 124 of the shaft section 123 projecting from the cylindersection 113. Thus, the assembly work involves screw fastening operation,resulting in a rather poor workability. Further, the number ofcomponents is large, resulting in a rather poor componentcontrollability.

Thus, in recent years, as a method for fastening the outer joint member103 of the constant velocity universal joint 104 and the hub wheel 102,there is proposed a method in which projections, which are provided onone of the outer surface of the shaft section 123 of the outer jointmember 103 and the inner surface of the hole of the hub wheel 102 so asto extend in an axial direction, are press-fitted to another one of theouter surface and the inner surface along the axial direction, andrecesses, which intimately fit on the projections, are formed in anotherone of the outer surface and the inner surface by the projections,whereby a recess-projection fitting structure is realized and theconstant velocity universal joint and the hub wheel are integrated witheach other. With this structure, it is possible to omit nut fasteningwork for integrating the hub wheel 102 and the constant velocityuniversal joint 104 with each other.

In the adhesion fitting method, the shaft section 123 as an innercomponent is press-fitted into the hub wheel 102 as an outer component,and hence the hub wheel 102 and the inner race 117 expand. Thisexpansion generates hoop stress on the raceway grooves (bearing racewaysurfaces) 118, 119, an inner race shoulder section 117 a, a section 133between the raceway grooves, and an inner race small-diameter outersection 134 of components. Here, the hoop stress means force forexpanding a diameter in the outer diameter direction. Therefore,excessive hoop stress causes trouble with the bearing. When the hoopstress is generated on the bearing raceway surfaces 118, 119, there is arisk that the hoop stress reduces rolling fatigue life and causesoccurrence of a crack. Further, the hoop stress is generated on theinner race 117 at a stage of press-fitting to the hub wheel 102 withinterference, and hence the hoop stress tends to be generatedparticularly on the second inner raceway surface 119 and the inner raceshoulder section 117 a. When the hoop stress is generated on the innerrace 117, there is a risk that stress corrosion crack occurs due to aninfluence of rust on the end surface portion exposed to outside.

As described above, if a large backlash occurs in a joint sectionbetween the hub wheel and the constant velocity universal joint orinside the constant velocity universal joint, noise, vibration, andharshness (NVH) (which are three factors for indicating comfortabilityof a vehicle) characteristics of a vehicle are deteriorated.Accordingly, in recent years, in order to improve the NVHcharacteristics, a demand for elimination of such a backlash is furtherrequired.

Further, in this bearing device for a wheel, at the time of assembly ofthe vehicle, the outer member of the roller bearing is internally fittedin a knuckle. In this case, the outer member and the knuckle arenormally integrated together by bolt fastening. Therefore, a backlasheasily occurs in the region fastened by the bolt.

In view of the above-mentioned problems, an object of the presentinvention is to provide a bearing device for a wheel that can realizeprevention of a backlash in a circumferential direction and is excellentin workability of connection of a hub wheel and an outer joint member ofa constant velocity universal joint. It is another object of the presentinvention to provide a bearing device for a wheel that can allowomission of nut fastening work and cost reduction, reduce generation ofhoop stress, and prevent occurrence of trouble with a bearing. It isstill another object of the present invention to provide a bearingdevice for a wheel that can prevent deterioration in NVHcharacteristics, which is caused by a backlash occurring in a jointsection between the hub wheel and the constant velocity universal jointor between an outer member and a knuckle, and can perform rotationtorque transmission with high accuracy.

Solution to Problems

A first bearing device for a wheel according to the present inventionincludes: a hub wheel; a constant velocity universal joint; and adouble-row roller bearing comprising: an outer member having an innercircumference in which double-row outer raceway surfaces are formed; aninner member including the hub wheel having an outer circumference inwhich one of inner raceway surfaces opposed to the double-row outerraceway surfaces is provided, and an inner race externally fitted ontothe hub wheel and having an outer circumference in which another one ofthe inner raceway surfaces opposed to the double-row outer racewaysurfaces is formed; and balls accommodated in double rows between boththe raceway surfaces of the inner member and the outer member so as tofreely roll, the hub wheel, the double-row roller bearing, and theconstant velocity universal joint being unitized together, wherein arecess-projection fitting structure, in which the hub wheel and a shaftsection of an outer joint member of the constant velocity universaljoint are integrated with each other, is provided, the recess-projectionfitting structure being configured such that projections, which areprovided on one of an outer surface of the shaft section of the outerjoint member and an inner surface of a hole of the hub wheel so as toextend in an axial direction, are press-fitted to another one of theouter surface and the inner surface along the axial direction, and thatrecesses, which intimately fit on the projections, are formed in anotherone of the outer surface and the inner surface by the projections, andthat entire regions of fitting contact regions between the projectionsand the recesses are brought into intimate contact with each other, andwherein fitting between the inner race and a small diameter step sectionin a range corresponding to an outer surface side of therecess-projection fitting structure is non-interference fitting, and thefitting between the inner race and the small diameter step section inanother range is interference fitting. Here, the interference fittingmeans fitting always involving interference in combination. Further, thenon-interference fitting means transition fitting or loose fitting.Further, the transition fitting means fitting involving a gap orinterference in combination due to actual dimensions of a hole and ashaft, and means fitting in which tolerance zones of the hole and theshaft entirely or partially overlap each other. The loose fitting meansfitting always involving a gap in combination.

According to the first bearing device for a wheel of the presentinvention, in the recess-projection fitting structure, the entirefitting contact regions between the projections and the recesses arebrought into intimate contact with each other. Therefore, in thisfitting structure, a gap in which a backlash occurs is not formed in adiameter direction and a circumferential direction.

Further, the fitting between the inner race and the small diameter stepsection in the range corresponding to the outer surface side of therecess-projection fitting structure is non-interference fitting, andhence it is possible to suppress at minimum generation of hoop stress ofthe inner race in the range corresponding to the outer surface side ofthe recess-projection fitting structure. The fitting between the innerrace and the small diameter step section in another range correspondingto the outer surface side of the recess-projection fitting structure isinterference fitting, and hence it is possible to prevent creep of theinner race. Here, the creep means a phenomenon of relative shift betweenfitting surfaces, which occurs when the bearing slightly moves in thecircumferential direction because of insufficiency of the interference,machining accuracy failure of the fitting surfaces, or the like and agap is generated between the fitting surfaces.

A circumferential notch section is formed in the inner surface of theinner race in the range corresponding to the outer surface side of therecess-projection fitting structure, whereby the non-interferencefitting may be performed. A circumferential notch section is formed inthe outer surface of the small diameter step section, whereby thenon-interference fitting may be performed.

There may be adopted a bearing device for a wheel in which a hub wheel,a double-row roller bearing, and a constant velocity universal joint areunitized together, and which has a recess-projection fitting structure,in which the hub wheel and a shaft section of an outer joint member ofthe constant velocity universal joint are integrated with each other. Inthe bearing device for a wheel, the recess-projection fitting structuremay be configured such that projections, which are provided on one of anouter surface of the shaft section of the outer joint member and aninner surface of a hole of the hub wheel so as to extend in an axialdirection, are press-fitted to another one of the outer surface and theinner surface along the axial direction, and that recesses, whichintimately fit on the projections, are formed in another one of theouter surface and the inner surface by the projections, and that entireregions of fitting contact regions between the projections and therecesses are brought into intimate contact with each other, and thedouble-row roller bearing includes the outer member having the racewaysurfaces at its inner circumference, the outer member being connected toa knuckle constituting a suspension device through an intermediation ofan integral connection structure of a non-separation type.

According to such a bearing device for a wheel, as in the case of thefirst bearing device for a wheel, in the recess-projection fittingstructure, the entire fitting contact regions between the projectionsand the recesses are brought into intimate contact with each other.Therefore, in this fitting structure, a gap in which a backlash occursis not formed in a diameter direction and a circumferential direction.Further, the knuckle constituting the suspension device is connected tothe outer member through an intermediation of the integral connectionstructure of the non-separation type, and hence a backlash does notoccur between the outer member and the knuckle. The integral connectionstructure may be configured by caulking at least one of the knuckle andthe outer member, by caulking a caulked member interposed between theknuckle and the outer member, or by welding the knuckle and the outermember together.

The projections of the recess-projection fitting structure are providedto the shaft section of the outer joint member of the constant velocityuniversal joint, and the recesses, which intimately fit on theprojections, are formed by the projections in the inner surface of thehole of the hub wheel by setting at least hardness of axial end portionsof the projections to be higher than that of an inner surface portion ofthe hole of the hub wheel, and by press-fitting the shaft section intothe hole of the hub wheel from a side of the axial end portions of theprojections, whereby the recess-projection fitting structure may beconfigured. In this case, the projections bite in the recess formationsurface of the opposite member (inner surface of hole of hub wheel),whereby the hole is slightly expanded in diameter and allows movement inthe axial direction of the projections. If the movement in the axialdirection stops, the hole decreases in diameter to return to theoriginal diameter. Thus, the entire recess fitting regions of theprojections are brought into intimate contact to the correspondingrecesses.

Further, the projections of the recess-projection fitting structure areprovided on the inner surface of the hole of the hub wheel, and therecesses, which intimately fit on the projections, are formed by theprojections in the outer surface of the shaft section of the outer jointmember by setting at least hardness of axial end portions of theprojections to be higher than that of an outer surface portion of theshaft section of the outer joint member of the constant velocityuniversal joint, and by press-fitting the projections on a side of thehub wheel to the shaft section of the outer joint member from a side ofthe axial end portions of the projections, whereby the recess-projectionfitting structure may be configured. The projections bite in the outersurface of the shaft section, whereby the hole of the hub wheel isslightly expanded in diameter and allows movement in the axial directionof the projections. If the movement in the axial direction stops, thehole decreases in diameter to return to the original diameter. Thus, theentire regions of the fitting contact regions between the projectionsand the recesses of the opposite member (outer surface of shaft), whichfit on the projections, are brought into intimate contact with eachother.

A second bearing device for a wheel according to the present inventionincludes: a hub wheel; a double-row roller bearing; and a constantvelocity universal joint, the hub wheel, the double-row roller bearing,and the constant velocity universal joint being unitized together, inwhich a recess-projection fitting structure, in which the hub wheel anda shaft section of an outer joint member of the constant velocityuniversal joint which is fitted and inserted into a hole of the hubwheel are integrated with each other, is provided, the recess-projectionfitting structure being configured such that entire regions of fittingcontact regions between projections on an outer surface of the shaftsection of the outer joint member and recesses, which fit on theprojections, in an inner surface of the hub wheel are brought intointimate contact with each other, and in which a hardened layer byinduction hardening is formed on an outer surface side of the hub wheel,and an inner surface side of the hub wheel is left in an unhardenedstate.

According to the second bearing device for a wheel according to thepresent invention, as in the case of the first bearing device for awheel, in the recess-projection fitting structure, the entire fittingcontact regions between the projections and the recesses are broughtinto intimate contact with each other. Therefore, in this fittingstructure, a gap in which a backlash occurs is not formed in a diameterdirection and a circumferential direction. Further, the inner surfaceside of the hub wheel is left in the unhardened state, and hence theinner surface side of the hub wheel is relatively soft. Therefore, it ispossible to realize improvement of fittability in fitting theprojections on the outer surface of the shaft section of the outer jointmember into the recesses in the inner surface of the hole of the hubwheel.

The hardened layer on the outer surface of the hub wheel is formed by,for example, induction hardening. Here, the induction hardening is ahardening method employing the principle of inserting a sectionnecessary to be hardened into a coil through which a high-frequencycurrent flows, generating Joule heat with an electromagnetic inductionaction, and heating a conductive substance. That is, if the inductionhardening is performed, the surface can be hard and its inside can bekept in hardness of a material. Therefore, the inner surface side of thehub wheel can be maintained in the unhardened state. In contrast, ifthere is used carburizing which is often used for performing hardeningtreatment on each region of the constant velocity universal joint, thereis a risk that the inner surface side is also hardened. That is, thecarburizing is a method of causing carbon to intrude/spread from thesurface of a low carbon material and performing hardening thereafter.Even if anti-carburizing treatment is performed, the inner surface sidecontains a certain amount of carbon and is hardened to about 400 HV.

Further, there may be adopted a bearing device for a wheel in which ahub wheel, a double-row roller bearing, and a constant velocityuniversal joint are unitized together, and which includes arecess-projection fitting structure, in which the hub wheel and a shaftsection of an outer joint member of the constant velocity universaljoint which is fitted and inserted into a hole of the hub wheel areintegrated with each other. In the bearing device for a wheel, therecess-projection fitting structure may be configured such that, bypress-fitting the shaft section of the outer joint member in a state ofheating and expanding in diameter the hole of the hub wheel, the entireregions of the fitting contact regions between the projections on theouter surface of the shaft section of the outer joint member and therecesses, which fit on the projections, in the inner surface of the hubwheel are brought into intimate contact with each other.

According to such a bearing device for a wheel, as in the case of thefirst bearing device for a wheel, in the recess-projection fittingstructure, the entire fitting contact regions between the projectionsand the recesses are brought into intimate contact with each other.Therefore, in this fitting structure, a gap in which a backlash occursis not formed in a diameter direction and a circumferential direction.Further, the shaft section of the outer joint member is press-fitted inthe state of heating and expanding in diameter the hole of the hubwheel, and hence the hole of the hub wheel decreases in diameter due toa decrease in temperature. In this case, a shape of the projections onthe outer surface of the shaft section is transferred onto the innersurface of the hub wheel. That is, the projections bite in the innersurface of the hub wheel, and this heating state is canceled. As aresult, the hole decreases in diameter to return to the originaldiameter. Accordingly, the entire regions of the fitting contact regionsbetween the projections and the recesses are brought into intimatecontact with each other.

It is preferred to set a heating expanding temperature to be lower thana guaranteed temperature for components of the bearing device for awheel. Here, the guaranteed temperature is a temperature at which therecan be exerted functions of the components (sealing, grease, cage,encoder, and the like) used in the bearing device for a wheel. If theheating expanding temperature is lower than this temperature, thefunctions of the components are not deteriorated.

Moreover, there may be adopted a bearing device for a wheel in which ahub wheel, a double-row roller bearing, and a constant velocityuniversal joint are unitized together, and which includes arecess-projection fitting structure, in which the hub wheel and a shaftsection of an outer joint member of the constant velocity universaljoint which is fitted and inserted into a hole of the hub wheel areintegrated with each other. In the bearing device for a wheel, therecess-projection fitting structure may be configured such that atapered section for centering, which decreases in diameter along apress-fitting direction, is formed to the hole of the hub wheel, andthat the shaft section of the outer joint member is press-fitted intothe hole of the hub wheel through an intermediation of the taperedsection, and that the entire regions of the fitting contact regionsbetween the projections on the outer surface of the shaft section of theouter joint member and the recesses, which fit on the projections, inthe inner surface of the hub wheel are brought into intimate contactwith each other.

According to such a bearing device for a wheel, as in the case of thefirst bearing device for a wheel, in the recess-projection fittingstructure, the entire fitting contact regions between the projectionsand the recesses are brought into intimate contact with each other.Therefore, in this fitting structure, a gap in which a backlash occursis not formed in a diameter direction and a circumferential direction.Further, the tapered section for centering, which decreases in diameteralong the press-fitting direction, is formed to the hole of the hubwheel. Accordingly, when the shaft section of the outer joint member ispress-fitted into the hole of the hub wheel, the tapered section forcentering can constitute a guide at the start of press-fitting.

It is preferred to provide a collar section for centering (cylindricalsurface section for centering) having a diameter equal to or slightlysmaller than the hole diameter of the hole of the hub wheel at theforward end of the shaft section of the outer joint member. When thecollar section is provided, it is possible to press-fit the shaftsection into the hub wheel while preventing decentering.

It is preferred to provide a pocket section that stores an extrudedportion caused by the recess formation by the press-fitting on the shaftsection. Here, the extruded portion is equivalent to a volume of amaterial in the recesses in which the recess fitting regions of theprojections are fitted. The extruded portion includes the materialextruded from the recesses to be formed, the material cut for formingthe recesses, or the material extruded and cut.

Further, projecting direction intermediate regions of the projectionscorrespond to a position of a recess forming surface of the hole of thehub wheel before recess formation. In this case, an inner diameterdimension of the inner surface of the hole of the hub wheel is set to besmaller than a maximum diameter dimension of a circle connectingvertexes of the projections, and to be larger than a maximum diameterdimension of the recesses in the outer surface of the shaft sectionamong the projections.

It is preferred to set circumferential thicknesses of projectingdirection intermediate regions of the projections to be smaller thancircumferential dimensions in positions corresponding to theintermediate regions in between the projections adjacent to one anotherin a circumferential direction. By this setting, a sum of thecircumferential thicknesses of the projecting direction intermediateregions of the projections is set to be smaller than a sum ofcircumferential thicknesses in positions corresponding to theintermediate regions in the projections on an opposite side that fit inbetween the projections adjacent to one another in the circumferentialdirection.

It is preferred to provide recess-projection portions along the axialdirection to at least the axial part of the member provided with theprojections. The recess-projection portions can be formed into a serrateshape.

The outer joint member of the constant velocity universal jointcomprises a mouth section in which an inner joint member is mounted, andthe shaft section provided so as to project from a bottom portion of themouth section, and, by caulking an end portion of the hub wheel, preloadis applied to the roller bearing through an intermediation of the innerrace of the roller bearing which is externally fitted onto the hubwheel, and the mouth section is out of contact with the end portion ofthe hub wheel.

Advantageous Effects of Invention

According to the present invention, in the recess-projection fittingstructure, a gap in which a backlash occurs is not formed in a diameterdirection and a circumferential direction. Thus, the entire fittingregions contribute to rotation torque transmission, and stable torquetransmission is possible. In addition, noise is not caused. Moreover,the entire fitting regions are brought into intimate contact with eachother with no gap, and hence strength of torque transmission regions isincreased. Therefore, the bearing device for a wheel can be reduced inweight and size.

Further, the fitting between the inner race and the small diameter stepsection in the range corresponding to the outer surface side of therecess-projection fitting structure is non-interference fitting, andhence it is possible to suppress at minimum generation of hoop stress ofthe inner race in the range corresponding to the outer surface side ofthe recess-projection fitting structure. Thus, it is possible to preventoccurrence of a trouble with a bearing such as a reduction in rollingfatigue life, occurrence of a crack, and stress corrosion crack, and toprovide a high-quality bearing device for a wheel.

The fitting between the inner race and the small diameter step sectionin another range corresponding to the outer surface side of therecess-projection fitting structure is interference fitting, and henceit is possible to prevent creep. That is, it is possible to prevent thecreep which is a phenomenon of relative shift between fitting surfaces,to secure stable fitting of the inner race, and to provide ahigh-quality bearing device for a wheel. Further, a circumferentialnotch section is formed in the inner surface of the inner race in therange corresponding to the outer surface side of the recess-projectionfitting structure, whereby the non-interference fitting may be formed. Acircumferential notch section is formed on the outer surface of thesmall diameter step section, whereby the non-interference fitting may beformed. As a result, it is possible to form a gap between the inner raceand the small diameter step section in this range, and to more reliablysuppress the generation of hoop stress. Further, when thecircumferential notch section is formed on the inner surface of theinner race, processing for forming the non-interference fitting on thehub wheel side is unnecessary, and there is an advantage that theexisting bearing device can be used. When the circumferential notchsection is formed on the outer surface of the small diameter stepsection, the processing for forming the non-interference fitting on theinner race side is unnecessary, and there is an advantage that theexisting bearing device can be used.

The knuckle is connected to the outer member through an intermediationof the integral connection structure of the non-separation type, andhence a backlash does not occur between the outer member and theknuckle. In addition, the outer member and the knuckle are integratedwith each other, and hence it is possible to realize simplification(facilitation) of assembly work in vehicle assembly plants. As describedabove, it is possible to reduce a backlash occurring on a joint sectionbetween the hub wheel and the constant velocity universal joint, and toeliminate a backlash between the outer member and the knuckle. Thus, itis possible to realize improvement of the NVH characteristics of avehicle which uses this bearing device for a wheel.

The inner surface side of the hub wheel is relatively soft. Therefore,it is possible to realize improvement of fittability (adhesiveness) infitting the projections on the outer surface of the shaft section of theouter joint member in the recesses in the inner surface of the hole ofthe hub wheel. It is possible to accurately suppress a backlash fromoccurring in the diameter direction and the circumferential direction.Moreover, the hardened layer is formed on the outer surface side of thehub wheel, and hence it is possible to realize improvement of strengthand durability of the hub wheel. In particular, the hardened layer isformed by the induction hardening, whereby hardening on the innersurface side is prevented and the unhardened state on the inner surfaceside is stably secured.

By press-fitting the shaft section of the outer joint member in a stateof heating and expanding in diameter the hole of the hub wheel, therecess-projection fitting structure can be configured reliably. Theheating expanding temperature is set to be lower than the guaranteedtemperature for components of the bearing device for a wheel.Accordingly, sealing, grease, and the like used in the bearing devicefor a wheel can exert their functions effectively, and a quality of thebearing device for a wheel can be guaranteed.

The tapered section for centering can constitute a guide at the start ofpress-fitting. Thus, it is possible to press-fit the shaft section ofthe outer joint member into the hole of the hub wheel without causingdecentering to thereby perform stable torque transmission. Inparticular, when the collar section for centering (cylindrical surfacesection for centering) is provided, it is possible to press-fit theshaft section into the hub wheel while preventing decentering, and hencemore stable press-fitting is possible.

The projections of the recess-projection fitting structure are providedin the shaft portion of the outer joint member of the constant velocityuniversal joint, the hardness of the axial ends of the projections isset to be higher than that of the inner surface portion of the hole ofthe hub wheel, and the shaft portion is press-fitted in the hole of thehub wheel from the axial end side. As a result, it is possible toincrease the hardness on the shaft portion side and improve the rigidityof the shaft portion by heat treatment. The projections of therecess-projection fitting structure are provided on the inner surface ofthe hole of the hub wheel, the hardness of the axial ends of theprojections is set to be higher than that of the outer surface portionof the shaft portion of the outer joint member of the constant velocityuniversal joint, and the projections on the hub wheel side arepress-fitted in the shaft portion of the outer joint member from theaxial end side thereof. As a result, it is unnecessary to performhardness treatment (heat treatment) on the shaft portion side.Therefore, the outer joint member of the constant velocity joint isexcellent in productivity.

By providing the pocket section for storing the extruded portion causedby recess formation by the press-fitting, it is possible to hold(maintain) the extruded portion in this pocket. The extruded portiondoes not enter the inside of the vehicle and the like on the outside ofthe device. In other words, it is possible to keep the extruded portionstored in the pocket section, it is unnecessary to perform removalprocessing for the extruded portion, and it is possible to realize areduction in assembly work man-hour and realize improvement of assemblyworkability and cost reduction.

By providing the collar section for centering with the hole of the hubwheel on the opposite projection side in the axial direction of thepocket section, ejection of the extruded portion in the pocket sectionto the collar section side is eliminated. The extruded portion is morestably stored. Moreover, the collar section is used for centering, andhence it is possible to press-fit the shaft portion into the hub wheelwhile preventing decentering. Therefore, it is possible to highlyaccurately connect the outer joint member and the hub wheel and performstable torque transmission.

Further, any regions in a projecting direction of the projections arearranged on a recess forming surface before recess formation, wherebythe projections bite in the recess forming surface during press-fitting.As a result, it is possible to reliably form the projections.

By setting the circumferential thicknesses of the projecting directionintermediate regions of the projections to be smaller than thedimensions in positions corresponding to the intermediate regions inbetween the projections adjacent to one another in the circumferentialdirection, it is possible to increase the circumferential thicknesses ofthe projecting direction intermediate regions of the projections on theside in which the recesses are formed (projections among the formedrecesses). Therefore, it is possible to increase a shearing area of theprojections on the opposite side (projections having low hardnessbetween the recesses because the recesses are formed) and secure torsionstrength. Moreover, tooth thicknesses of the projections on the highhardness side are small, and hence it is possible to reducepress-fitting load and realize improvement of press-fitting properties.

By providing recess-projection portions on a side of the projections,the recess-projection portions bite into a member having smallerhardness (member provided with the recesses in which the projectionsfit) along the axial direction during press-fitting. Owing to thisbiting-in, it is possible to form slipping-off in the axial direction ofthe outer joint member of the constant velocity universal joint withrespect to the hub wheel. Thus, it is possible to maintain a stableconnected state, and to realize improvement of a quality of the bearingdevice for a wheel. In addition, slipping-off can be formed by therecess-projection portions, and hence screw fastening in the prior artcan be omitted. Therefore, it is unnecessary to form, in the shaftsection, a screw section projecting from the hole of the hub wheel. Itis possible to realize a reduction in weight, to omit screw fasteningwork, and to realize improvement of assembly workability.

A mouth section is out of contact with the end portion of the hub wheel,and hence it is possible to prevent generation of noise due to contactbetween the mouth section and the hub wheel. Note that, if it ispossible to suppress the generation of noise, the mouth section and acaulked section of the hub wheel may be held in contact with each other.Further, the end portion of the hub wheel is caulked and preload isapplied to the roller bearing, and hence it is unnecessary to apply thepreload to the roller bearing by the mouth section of the outer jointmember. Thus, without taking the preload to the roller bearing intoconsideration, it is possible to press-fit the shaft section of theouter joint member, and to realize improvement of connectability(assemblability) between the hub wheel and the outer joint member.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal sectional view of a bearing device for a wheelaccording to a first embodiment of the present invention;

FIG. 2A is an enlarged sectional view illustrating a recess-projectionfitting structure of the bearing device for a wheel;

FIG. 2B is an enlarged view of an X section of FIG. 2A, illustrating therecess-projection fitting structure of the bearing device for a wheel;

FIG. 3 is a sectional view illustrating a state in which the bearingdevice for a wheel is disassembled;

FIG. 4 is an enlarged sectional view of a main part of arecess-projection fitting structure according to a modification;

FIG. 5 is a longitudinal sectional view of a bearing device for a wheelaccording to a second embodiment of the present invention;

FIG. 6 is an enlarged sectional view of a main part of FIG. 5;

FIG. 7 is an enlarged view of a main part of a hub wheel of the bearingdevice for a wheel illustrated in FIG. 1;

FIG. 8 is a simplified view of a shaft section of an outer race of aconstant velocity universal joint according to a modification;

FIG. 9 is a simplified view illustrating a state in which the shaftsection of the constant velocity universal joint illustrated in FIG. 8is press-fitted into the hub wheel;

FIG. 10 is an enlarged sectional view of a main part of FIG. 9;

FIG. 11 is an enlarged view of a main part of a hub wheel according to acomparative example;

FIG. 12 is an enlarged sectional view of a main part of a bearing devicefor a wheel according to a third embodiment of the present invention;

FIG. 13 is an enlarged sectional view of a main part of a bearing devicefor a wheel according to a modification of the present invention;

FIG. 14 is an enlarged sectional view of a main part of a bearing devicefor a wheel according to another modification of the present invention;

FIG. 15 is an enlarged sectional view of a main part of a bearing devicefor a wheel according to a fourth embodiment of the present invention;

FIG. 16A is an enlarged sectional view illustrating an integralconnection structure before a fixing member is caulked;

FIG. 16B is an enlarged sectional view illustrating the integralconnection structure after the fixing member is caulked;

FIG. 17 is a sectional view illustrating a state in which the bearingdevice for a wheel illustrated in FIG. 15 is disassembled;

FIG. 18A is a sectional view illustrating an integral connectionstructure according to a modification in a case of using welding;

FIG. 18B is a sectional view illustrating the integral connectionstructure according to a modification in a case of not using the fixingmember;

FIG. 19 is a sectional view of a hole of a hub wheel according to amodification;

FIG. 20 is an enlarged sectional view of a hole of a hub wheel accordingto another modification;

FIG. 21A is an enlarged sectional view of a main part of a bearingdevice for a wheel according to a fifth embodiment of the presentinvention;

FIG. 21B is an enlarged view of a Y section of FIG. 21A; and

FIG. 22 is a sectional view of a conventional bearing device for awheel.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention are described below with referenceto FIGS. 1 to 21. A bearing device for a wheel according to a firstembodiment is illustrated in FIG. 1. In this bearing device for a wheel,a hub wheel 1, a double-row roller bearing 2, and a constant velocityuniversal joint 3 are united together.

The constant velocity universal joint 3 mainly includes an outer race 5as an outer joint member, an inner race 6 as an inner joint memberarranged on the inner side of the outer race 5, multiple balls 7provided between the outer race 5 and the inner race 6 to transmittorque, and a cage 8 provided between the outer race 5 and the innerrace 6 to retain the balls 7. An end portion 10 a of a shaft 10 ispress-fitted into a shaft hole inner diameter 6 a of the inner race 6 toeffect spline fitting, whereby connection with the shaft 10 is effectedso as to allow torque transmission. A stop ring 9 for preventing shaftslipping-off is fitted in the end portion 10 a of the shaft 10.

The outer race 5 includes a mouth section 11 and a shaft section (shaftsection) 12, and the mouth section 11 is formed in a cup-like shape openat its one end. In an inner spherical surface 13 thereof, there areformed multiple axially extending track grooves 14 at equalcircumferential intervals. The track grooves 14 extend to the open endof the mouth section 11. The inner race 6 has in an outer sphericalsurface 15 thereof multiple axially extending track grooves 16 formed atequal circumferential intervals.

The track grooves 14 of the outer race 5 and the track grooves 16 of theinner race 6 are paired with each other, and one ball 7 as a torquetransmission element is incorporated into a ball track formed by eachpair of track grooves 14 and 16 so as to be capable of rolling. Theballs 7 are provided between the track grooves 14 of the outer race 5and the track grooves 16 of the inner race 6 to transmit torque. Thecage 8 is slidably provided between the outer race 5 and the inner race6, with an outer spherical surface 8 a thereof coming into contact withthe inner spherical surface 13 of the outer race 5 and an innerspherical surface 8 b thereof coming into contact with the outerspherical surface 15 of the inner race 6. While in this case theconstant velocity universal joint is of the undercut free type, in whicheach of the track grooves 14 and 16 has a linear straight sectionprovided to a groove bottom, it is also possible to adopt a constantvelocity universal joint of some other type such as the Rzeppa type.

The hub wheel 1 has a cylinder section 20 and a flange 21 provided to anend portion on an opposite joint side of the cylinder section 20. A hole22 of the cylinder section 20 includes a shaft section fitting hole 22 aformed at an intermediate section in an axial direction, a tapered hole22 b on the opposite joint side, and a large diameter hole 22 c on ajoint side. That is, in the shaft section fitting hole 22 a, the shaftsection 12 of the outer race 5 of the constant velocity universal joint3 and the hub wheel 1 are connected to each other through anintermediation of a recess-projection fitting structure M describedlater. Further, between the shaft section fitting hole 22 a and thelarge diameter hole 22 c, a tapered section (tapered hole) 22 d isprovided. The tapered section 22 d decreases in diameter along apress-fitting direction when the hub wheel 1 and the shaft section 12 ofthe outer race 5 are connected to each other. A tapered angle θ (seeFIG. 7) of the tapered section 22 d is set to, for example, 15° to 75°.

The roller bearing 2 includes an inner race 24 that fit in a smalldiameter step section 23 provided on the joint side of the cylindersection 20 of the hub wheel 1 and an outer member 25 provided on anouter circumferential side of the cylinder section 20 of the hub wheel1. In the outer member 25, outer raceway surfaces (outer races) 26 and27 in two rows are provided on an inner circumference thereof. The firstouter raceway surface 26 and a first inner raceway surface (inner race)28 provided on an outer circumference of the cylinder section 20 of thehub wheel 1 are opposed to each other. The second outer raceway surface27 and a second inner raceway surface (inner race) 29 provided on anouter circumferential surface of the inner race 24 are opposed to eachother. Balls as rolling elements 30 are interposed between the firstouter raceway surface 26 and the first inner raceway surface 28 andbetween the second outer raceway surface 27 and the second inner racewaysurface 29. Seal members S1 and S2 are inserted in both openings of theouter member 25.

In this case, the end on the joint side of the hub wheel 1 is caulked,whereby preload is applied to the roller bearing 2. Consequently, theinner race 24 can be fastened to the hub wheel 1. Further, a boltinserting hole 32 is provided in the flange 21 of the hub wheel 1, and ahub bolt 33 for fixing a wheel and a brake rotor to the flange 21 isinserted into the bolt inserting hole 32.

As illustrated in FIG. 2A, the recess-projection fitting structure M isformed, for example, of axially extending projections 35 provided to theshaft portion 12, and recesses 36 formed in the inner surface of thehole section 22 of the hub wheel 1 (inner surface 37 of the shaftsection fitting hole 22 a in this case). The entire regions of thefitting contact regions 38 of the projections 35 and the recesses 36 ofthe hub wheel 1 fitted in the projections 35 are held in close contact.In other words, multiple projections 35 are arranged at a predeterminedcircumferential pitch on the outer peripheral surface of the oppositemouth section side of the shaft portion 12, and multiple recesses 36 tobe fitted in the projections 35 are formed circumferentially in theinner surface 37 of the shaft section fitting hole 22 a of the hole 22of the hub wheel 1. That is, over the circumferential entire periphery,the projections 35 and the recesses 36 fit-engaged thereto are tightlyfitted in each other.

In this case, the respective projections 35 are formed in a triangularshape (ridge shape) having a vertex of a projected R shape in section.Recess fitting contact regions of the projections 35 are ranges 75illustrated in FIG. 2B and ranges from halfway sections of the ridges insection to the tops of the ridges. A gap 40 is formed further on aninner surface side than an inner surface 37 of the hub wheel 1 betweenthe projections 35 adjacent to each other in the circumferentialdirection.

In this way, the hub wheel 1 and the shaft portion 12 of the outer race5 of the constant velocity universal joint 3 can be connected through anintermediation of the recess-projection fitting structure M. In thiscase, the end on the joint side of the hub wheel 1 is caulked andpreload is applied to the roller bearing 2 by the caulked section 31,and hence it is unnecessary to apply preload to the roller bearing 2 inthe mouth section 11 of the outer race 5, whereby the mouth section 11is out of contact with the end of the hub wheel 1 (in this case, caulkedsection 31).

According to the present invention, in the recess-projection fittingstructure M, the entire regions of the fitting contact regions 38between the projections 35 and the recesses 36 are held in closecontact, and hence a gap in which a backlash occurs is not formed in adiameter direction and a circumferential direction. Thus, the entirefitting regions contribute to rotation torque transmission, and stabletorque transmission is possible. In addition, noise is not generated.

The mouth section 11 is out of contact with the hub wheel 1, in otherwords, a gap t1 (see FIG. 1) is provided between a bottom wall outersurface 11 a of the mouth section 11 and the outer surface of thecaulked section 31, and hence it is possible to suppress generation ofnoise due to contact between the mouth section 11 and the hub wheel 1.In the present invention, if it is possible to prevent the generation ofnoise, the mouth section 11 and the caulked section 31 of the hub wheel1 may be held in contact with each other. Further, the end portion ofthe hub wheel 1 is caulked and preload is applied to the roller bearing2, and hence it is unnecessary to apply the preload to the rollerbearing 2 by the mouth section 11 of the outer joint member. Thus,without taking the preload to the roller bearing 2 into consideration,it is possible to press-fit the shaft section 12 of the outer jointmember, and to realize improvement of connectability (assemblability)between the hub wheel 1 and the outer joint member.

A method of fitting the recess-projection fitting structure M isdescribed. In this case, as illustrated in FIG. 3, thermal hardeningtreatment is performed an outer surface portion of the shaft portion 12.The spline 41 including projections 41 a and recesses 41 b along theaxial direction is formed in this hardened layer H. Therefore, theprojections 41 a of the spline 41 are hardened and change to theprojections 35 of the recess-projection fitting structure M. A range ofthe hardened layer H in this embodiment is, as indicated by a crosshatching section, from an outer edge of the spline 41 to a part of abottom wall of the mouth section 11 of the outer race 5. As this thermalhardening treatment, various kinds of heat treatment such as inductionhardening and carburizing can be adopted. The induction hardening is ahardening method employing the principle of inserting a sectionnecessary for hardening into a coil through which a high-frequencycurrent flows, generating Joule heat with an electromagnetic inductionaction, and heating a conductive substance. The carburizing is a methodof causing carbon to intrude/spread from the surface of a low carbonmaterial and performing hardening after that. The teeth of the spline 41of the shaft section 12 have a module equal to or smaller than 0.5.Here, the module is a ratio of a pitch diameter of the spline divided bythe number of teeth.

Further, a hardened layer H1 by the induction hardening is formed on theouter surface side of the hub wheel 1 and the inner surface side of thehub wheel 1 is left in an unhardened state. A range of the hardenedlayer H1 in this embodiment is, as indicated by a cross hatchingsection, from the base section of the flange 21 to near the caulkedsection of the step section 23 in which the inner race 24 fits. If theinduction hardening is performed, the surface can be hard and its insidecan be kept in hardness of a material. Therefore, the inner surface sideof the hub wheel 1 can be maintained in the unhardened state. The innersurface 37 side of the hole 22 of the hub wheel 1 is an unhardenedsection not subjected to the thermal hardening treatment (in anunhardened state). A hardness difference between the hardened layer H ofthe shaft section 12 of the outer race 5 and the unhardened section ofthe hub wheel 1 is set to be equal to or larger than 30 points in HRC.

In this case, a projecting direction intermediate region of theprojections 35 corresponds to a position of a recess forming surfacebefore recess formation (in this case, inner surface 37 of the hole 22of the hub wheel 1). That is, an inner diameter dimension D of the innersurface 37 of the shaft section fitting hole 22 a of the hole 22 is setto be smaller than a maximum outer diameter of the projections 35, i.e.,a maximum diameter dimension (circumscribed circle diameter) D1 of acircle connecting vertexes of the projections 35 as the projections 41 aof the spline 41 and is set to be larger than an outer diameterdimension of a shaft section outer surface among the projections, i.e.,a maximum diameter dimension D2 of a circle connecting bottoms of therecesses 41 b of the spline 41. In other words, the dimensions are setin a relation of D2<D<D1.

The spline 41 can be formed by various machining methods such ascomponent rolling, cutting, pressing, and drawing, which are publiclyknown and used conventional means. As the thermal hardening treatment,various kinds of heat treatment such as induction hardening andcarburizing can be adopted.

Then, as illustrated in FIG. 3, the shaft section 12 of the outer race 5is inserted (press-fit) into the hub wheel 1 in a state in which theaxis of the hub wheel 1 and the axis of the outer race 5 of the constantvelocity universal joint 3 are aligned. In this case, the diameterdimension D of the inner surface 37 of the hole 22, the maximum outerdiameter dimension D1 of the projections 35, and the minimum outerdiameter dimension D2 of the recesses of the spline 41 are in therelation described above. Moreover, the hardness of the projections 35is larger than the hardness of the inner surface 37 of the hole 22 by 30points or more. Therefore, if the shaft section 12 is press-fitted intothe hole 22 of the hub wheel 1, the projections 35 bite in the innersurface 37, and the projections 35 form the recesses 36, in which theprojections 35 fit, along the axial direction.

Thus, as illustrated in FIGS. 2A and 2B, the entire fitting contactregions 38 of the projections 35 at the end of the shaft portion 12 andthe recesses 36 fit therein are brought into intimate contact with eachother. In other words, a shape of the projections 35 is transferred ontoa recess formation surface on the opposite side (in this case, the innersurface 37 of the hole 22). When the shape is transferred, because theprojections 35 bite in the inner surface 37 of the hole 22, the hole 22is slightly expanded in diameter and allows movement in the axialdirection of the projections 35. If the movement in the axial directionstops, the hole 22 decreases in diameter to return to the originaldiameter. In other words, the hub wheel 1 is elastically deformed in thediameter direction when the projections 35 are press-fitted, and preloadequivalent to this elastic deformation is applied to a tooth surface ofthe projections 35 (surface of the recess fitting region). Therefore, itis possible to surely form the recess-projection fitting structure M inwhich the entire recess fitting regions of the projections 35 arebrought into intimate contact to the recesses 36 corresponding thereto.Moreover, it is unnecessary to form spline sections and the like in amember (in this case, the hub wheel 1) in which the recesses 36 areformed. The bearing device for a wheel is excellent in productivity.Further, phase alignment of the splines is unnecessary. It is possibleto realize improvement of assemblability, prevent damage to the toothsurfaces during press-fitting, and maintain a stable fit state.

As in the above-mentioned embodiment, teeth with a module equal to orsmaller than 0.5 are used in the spline 41 formed in the shaft portion12. Therefore, it is possible to realize improvement of moldability ofthis spline 41 and realize a reduction in press-fitting load. Becausethe projections 35 can be formed by a spline normally formed in theshaft of this kind, it is possible to easily form the projections 35 atlow cost.

When the recesses 36 are formed by press-fitting the shaft portion 12into the hub wheel 1, work hardening occurs on the recesses 36 side. Thework hardening means that, when plastic deformation (plastic working) isapplied to an object, resistance against deformation increases as adegree of deformation increases and the object becomes harder than amaterial not subjected to deformation. Therefore, according to plasticdeformation during press-fitting, the inner surface 37 of the hub wheel1 on the recesses 36 side hardens. It is possible to realize improvementof rotation torque transmission performance.

The inner surface side of the hub wheel 1 is relatively soft. Therefore,it is possible to realize improvement of fittability (adhesiveness) infitting the projections 35 of the outer surface of the shaft portion 12of the outer race 5 in the recesses 36 of the hole inner surface of thehub wheel 1. It is possible to accurately suppress a backlash fromoccurring in the diameter direction and the circumferential direction.Moreover, the hardened layer H1 is formed on the outer surface side ofthe hub wheel 1, and hence it is possible to realize improvement ofstrength and durability of the hub wheel 1. In particular, the hardenedlayer H1 is formed by the induction hardening, whereby hardening on theinner surface side is prevented and the unhardened state on the innersurface side is stably secured.

By the way, in the spline 41 illustrated in FIG. 3, the pitch of theprojections 41 a and the pitch of the recesses 41 b are set to the samevalue. Thus, in the above-mentioned embodiment, as illustrated in FIG.2B, a circumferential thickness L of projecting direction intermediateregions of the projections 35, and a circumferential dimension L0 in aposition corresponding to the intermediate region between theprojections 35 adjacent to each other in the circumferential directionare substantially the same.

On the other hand, as illustrated in FIG. 4, a circumferential thicknessL2 of the projecting direction intermediate regions of the projections35 may be smaller than a circumferential dimension L1 in a positioncorresponding to the intermediate region between the projections 35adjacent to each other in the circumferential direction. In other words,in the spline 41 formed in the shaft portion 12, the circumferentialthickness (tooth thickness) L2 of the projecting direction intermediateregions of the projections 35 is set to be smaller than thecircumferential thickness (tooth thickness) L1 of projecting directionintermediate regions of projections 43 on the hub wheel 1 side, that fitin between the projections 35.

Therefore, a sum Σ(B1+B2+B3+ . . . ) of tooth thicknesses of theprojections 35 in the entire circumference on the shaft portion 12 sideis set to be smaller than a sum Σ(A1+A2+A3+ . . . ) of tooth thicknessesof the projections 43 (projecting teeth) on the hub wheel 1 side.Consequently, it is possible to increase a shearing area of theprojections 43 on the hub wheel 1 side and secure torsion strength.Moreover, the tooth thickness of the projections 35 is small, and henceit is possible to reduce press-fitting load and realize improvement ofpress-fitting performance. When a sum of circumferential thicknesses ofthe projections 35 is set to be smaller than a sum of circumferentialthicknesses of the projections 43 on the opposite side, it isunnecessary to set the circumferential thickness L2 of all theprojections 35 smaller than the dimension L1 in the circumferentialdirection between the projections 35 adjacent to each other in thecircumferential direction. In other words, even if the circumferentialthickness of arbitrary projections 35 among the multiple projections 35is the same as or larger than a dimension in the circumferentialdirection between the projections adjacent to each other in thecircumferential direction, a sum of circumferential thicknesses only hasto be smaller than a sum of dimensions in the circumferential direction.Note that a sectional shape of the projections 35 in FIG. 4 aretrapezoidal.

Further, when the shaft section 12 of the outer race 5 is press-fittedinto the hole 22 of the hub wheel 1, the tapered section 22 d forcentering can constitute a guide at the start of press-fitting. Thus, itis possible to press-fit the shaft section 12 of the outer race 5 intothe hole 22 of the hub wheel 1 without causing decentering to therebyperform stable torque transmission.

In comparison thereto, as illustrated in FIG. 11, in the case where, inthe hole 22 of the hub wheel 1, the tapered section 22 d is not formedbetween the fitting hole 22 a and the large diameter hole 22 c but astep section 22 e is formed therebetween, centering can not be performedwhen the shaft section 12 of the outer race 5 is press-fitted into thehole 22 of the hub wheel 1, and hence there is a risk of causingdecentering between the hub wheel 1 and the outer race 5 of the constantvelocity universal joint 3. Therefore, it is preferred to set theinclination angle θ (see FIG. 7) of the tapered section 22 d to 15° to75° as described above. That is, if the inclination angle is less than15°, the tapered section 22 d can exert a function as the guide.However, the axial length of the tapered section 22 d is elongated,whereby workability of press-fitting is deteriorated, and there is arisk that the axial length of the hub wheel 1 is elongated. Further, ifthe inclination angle exceeds 75°, as in the case of forming the stepsection 22 e as illustrated in FIG. 11, there is a risk of causingdecentering.

Incidentally, when the shaft section 12 of the outer race 5 ispress-fitted into the hub wheel 1, a material is extruded from therecesses 36 formed by the projections 35, and an extruded portion 45according to a second embodiment illustrated in FIG. 5 is formed. Theextruded portion 45 is equivalent to a volume of the material of therecesses 36 in which recess fitting regions of the projections 35 arefitted. The extruded portion 45 includes the material extruded from therecesses 36 to be formed, the material cut for forming the recesses 36,or the material extruded and cut.

Therefore, in the bearing device for a wheel illustrated in FIG. 1,removal work for the extruded portion 45 is required after the constantvelocity universal joint is assembled to the hub wheel 1. Thus, in thisembodiment, as described above, a pocket section 50 for storing theextruded portion 45 is provided to the shaft section 12.

The pocket section 50 is formed by providing a circumferential groove 51at the shaft edge of the spline 41 of the shaft section 12. Asillustrated in FIG. 6, in the circumferential groove 51, a side wall 51a on the spline 41 side is a plane orthogonal to the axial direction,and a side surface 51 b on an opposite spline side is a tapered surfacethat expands in diameter from a groove bottom 51 c to the oppositespline side.

Further, a disc-like collar section 52 for centering is provided furtheron the opposite spline side with respect to the side surface 51 b. Anouter diameter dimension D4 of the collar section 52 is set the same asor slightly smaller than the hole diameter of the fitting hole 22 a ofthe hole 22. In this case, a very small gap t is provided between anouter surface 52 a of the collar section 52 and the inner surface of thefitting hole 22 a of the hole 22.

When the shaft section 12 is press-fitted into the hole 22 of the hubwheel 1, as illustrated in FIG. 6, the extruded portion 45 to be formedis stored in the pocket section 50 while curling. In other words, a partof the material scraped off or extruded from the inner surface of thehole 22 enters the pocket section 50.

By providing the pocket section 50 for storing the extruded portion 45caused by recess formation by the press-fitting, it is possible to hold(maintain) the extruded portion 45 in this pocket section 50. Further,the extruded portion 45 does not enter the inside of the vehicle and thelike on the outside of the device. In other words, the extruded portion45 can be kept stored in the pocket section 50. It is unnecessary toperform removal processing for the extruded portion 45. It is possibleto realize a reduction in assembly work man-hour and realize improvementof assembly workability and cost reduction.

Further, by providing, in the axial direction of the pocket section 50,the collar section 52 for centering with the hole 22 of the hub wheel 1on the opposite projection side, ejection of the extruded portion 45 inthe pocket section 50 to the collar section 52 side is eliminated.Therefore, the extruded portion 45 is more stably stored. Moreover, thecollar section 52 is used for centering, and hence it is possible topress-fit the shaft portion 12 into the hub wheel 1 while preventingdecentering. Therefore, it is possible to highly accurately connect theouter race 5 and the hub wheel 1 and to perform stable torquetransmission.

The collar section 52 is used for centering during press-fitting, andhence it is preferred to set an outer diameter dimension thereof to adegree slightly smaller than a hole diameter of the fitting hole 22 a ofthe hole 22 of the hub wheel 1. If the outer diameter dimension of thecollar section 52 is the same as or larger than the hole diameter of thefitting hole 22 a, the collar section 52 itself is press-fitted into thefitting hole 22 a. When the collar section 52 is press-fitted into thefitting hole 22 a, if the collar section 52 and the fitting hole 22 aare decentered, the projections 35 of the recess-projection fittingstructure M are press-fitted in this state and the shaft portion 12 andthe hub wheel 1 are connected in a state in which the axis of the shaftportion 12 and the axis of the hub wheel 1 are not aligned. If the outerdiameter dimension of the collar section 52 is too smaller than the holediameter of the fitting hole 22 a, the collar section 52 does notfunction as a section for centering. Therefore, it is preferred to setthe very small gap t between the outer surface 52 a of the collarsection 52 and the inner surface of the fitting hole 22 a of the hole 22to about 0.01 mm to 0.2 mm.

As the recess-projection fitting structure M, serrate recess-projectionportions 55 may be formed in the projections 35 of the shaft section 12,that is, in the projections 41 a of the spline 41. The recess-projectionportions 55 are small recess-projection portions formed along thelongitudinal direction of tops of the projections 41 a. In this case, asectional shape of projections (projected teeth) 55 a is a right-angledtriangle having a side inclined to the pocket side. Therecess-projection portions 55 in the figure are provided on the pocketsection 50 side.

As illustrated in FIG. 8, when the shaft section 12 provided with therecess-projection portions 55 is press-fitted into the hole 22 of thehub wheel 1, as illustrated in FIG. 9, while centering is performed bythe collar section 52, the recesses 36 are formed on the hub wheel 1side by the projections 35 on the shaft section 12 side, whereby theextruded portion 45 is formed. Then, the extruded portion 45 is storedin the pocket section 50 while curling.

Further, during the press-fitting, the recess-projection portions 55bite in the bottom portions of the recesses 36 formed on the hub wheel 1side. In other words, the hole 22 of the hub wheel 1, which has expandedin diameter, expands in diameter during press-fitting, whereas the hole22 of the hub wheel 1 decreases in diameter so as to return its originalstate upon completion of the press-fitting. Thus, pressing force (forcefor decreasing in diameter) acts on the recess-projection portions 55from the inner surface side of the hole 22 of the hub wheel 1 asindicated by arrows of FIG. 10, and the projections 55 a of therecess-projection portions 55 bite in the inner surface of the hole 22of the hub wheel 1.

As described above, by providing the recess-projection portions (serrateportions) 55 on the projections 35 side, the projections 55 a of theserrate portions 55 bite in along the axial direction duringpress-fitting. Owing to this biting-in, it is possible to formslipping-off in the axial direction of the outer joint member 5 of theconstant velocity universal joint with respect to the hub wheel 1.Consequently, it is possible to maintain a stable connected state andrealize improvement of a quality of the bearing device for a wheel. Inaddition, slipping-off can be formed by the serrate portions 55, andhence screw fastening in the prior art can be omitted. Therefore, it isunnecessary to form the screw section projecting from, in the shaftsection 12, the hole 22 of the hub wheel 1. It is possible to realize areduction in weight, omit screw fastening work, and realize improvementof assembly workability.

In the above-mentioned bearing device for a wheel, as illustrated inFIG. 12 according to a third embodiment, it is preferred that fittingbetween the inner race 24 and the small diameter step section 23 in arange 78 corresponding to the outer surface side of therecess-projection fitting structure M is non-interference fitting, andfitting between the inner race 24 and the small diameter step section 23in another range 79 is interference fitting. Here, the interferencefitting means fitting always involving interference in combination.Further, the non-interference fitting means transition fitting or loosefitting. Further, the transition fitting means fitting involving a gapor interference in combination due to actual dimensions of a hole and ashaft (hole diameter of hub wheel 1 and outer diameter of stem shaft12), and means fitting in which tolerance zones of the hole and theshaft (tolerance zones of hole diameter of hub wheel 1 and outerdiameter of stem shaft 12) entirely or partially overlap each other. Theloose fitting means fitting always involving a gap in combination.

The fitting between the inner race 24 and the small diameter stepsection 23 in the range corresponding to the outer surface side of therecess-projection fitting structure M is non-interference fitting, andhence it is possible to suppress at minimum generation of hoop stress ofthe inner race in the range corresponding to the outer surface side ofthe recess-projection fitting structure M. Thus, it is possible toprevent occurrence of a trouble with the bearing such as a reduction inrolling fatigue life, occurrence of a crack, and stress corrosion crack,and to provide a high-quality bearing device for a wheel. Further, thefitting between the inner race 24 and the small diameter step section 23in another range corresponding to the outer surface side of therecess-projection fitting structure M is interference fitting.Accordingly, it is possible to prevent creep which is a phenomenon ofrelative shift between fitting surfaces, to secure stable fitting of theinner race 24, and to more stably provide a high-quality bearing devicefor a wheel.

As illustrated in FIG. 13, a circumferential notch section 80 is formedon the inner surface of the inner race in the range 78 corresponding tothe outer surface side of the recess-projection fitting structure M, andthe non-interference fitting (loose fitting, in this case) may be formedtherein.

Other components of the bearing device for a wheel illustrated in FIG.13 are the same as those of the bearing device illustrated in FIGS. 1and 2. Thus, the components same as those illustrated in FIGS. 1 and 2are denoted by the same reference symbols and description of thecomponents is omitted.

Therefore, the bearing device illustrated in FIG. 13 also realizesoperations and effects same as those of the bearing device illustratedFIGS. 1 and 2. In particular, the circumferential notch section 80 isformed on the inner surface of the inner race, and the non-interferencefitting is formed, whereby it is possible to form the gap between theinner race 24 and the small diameter step section 23 in this range, andto more reliably suppress the generation of hoop stress. Further,processing is not required for forming the non-interference fitting tothe hub wheel side, and there is an advantage that the existing bearingdevice can be used.

Further, as illustrated in FIG. 14, a circumferential notch section 81is formed on the outer surface of the small diameter step section 23 ofthe hub wheel 1 in the range 78 corresponding to the outer surface sideof the recess-projection fitting structure M, and the non-interferencefitting (transition fitting, in this case) may be formed therein.

Other components of the bearing device for a wheel illustrated in FIG.14 are the same as those of the bearing device illustrated in FIGS. 1and 2. Thus, the components same as those illustrated in FIGS. 1 and 2are denoted by the same reference symbols and description of thecomponents is omitted.

Therefore, the bearing device illustrated in FIG. 14 also realizesoperations and effects same as those of the bearing device illustratedFIGS. 1 and 2. In particular, the circumferential notch section 81 isformed on the outer surface of the small diameter step section 23, andthe non-interference fitting is formed, whereby it is possible to formthe gap between the inner race 24 and the small diameter step section 23in this range, and to more reliably suppress the generation of hoopstress. Further, processing is not required for forming thenon-interference fitting to the inner race 24 side, and there is anadvantage that the existing bearing device can be used.

Incidentally, as illustrated in FIGS. 15, 16A, and 16B according to afourth embodiment, in the bearing device for a wheel of this type, aknuckle N is connected to the outer member 25 of the roller bearing 2through an intermediation of an integral connection structure 85 of anon-separation type. The integral connection structure 85 in this caseincludes a fixing member 86 serving as a caulked member caused to bebrought into intimate contact to the outer surface of the outer member25, and the knuckle N is externally fitted onto the fixing member 86.The fixing member 86 includes a short cylinder-shaped main body section87 fit onto the outer member 25, and outer collar portions 88 a, 88 bprovided at the axial end portions of the main body section 87.

In this case, a circumferential groove 89 is provided at theintermediate position in the axial direction on the outer surface of theouter member 25, and an inwardly projecting portion 93 is provided atthe intermediate position in the axial direction on the inner surface ofthe main body section 87 of the fixing member 86. Then, in the state inwhich the inwardly projecting portion 93 is fitted in thecircumferential groove 89, the outer member 25 and the fixing member 86are integrated with each other. In the state in which the knuckle N isexternally fitted onto the main body section 87, the outer collarportions 88 a, 88 b are locked to end surfaces 90 a, 90 b (see FIGS. 16Aand 16B) of a boss section 90 having a fitting hole 92 of the knuckle N.

That is, before mounting of the knuckle, axial end portions 86 a, 86 bof the fixing member 86 project outwardly in the axial direction fromaxial edges of the outer member 25. Then, at the time of mounting of theknuckle, plastic working (caulking working) is performed such that theaxial end portions 86 a, 86 b of the fixing member 86 project in theouter diameter direction. In this case, the caulking working may beperformed on the entire or part of the circumference. With this, theknuckle N is fixed to the outer member 25 through an intermediation ofthe fixing member 86.

Also in this case, as illustrated in FIG. 17, in the state in which theaxis of the hub wheel 1 and the axis of the outer race 5 of the constantvelocity universal joint 3 are aligned, the shaft section 12 ispress-fitted into the hole 22 of the hub wheel 1.

The knuckle N is connected to the outer member 25 through anintermediation of the integral connection structure 85 of thenon-separation type, and hence a backlash does not occur between theouter member 25 and the knuckle N. Moreover, the outer member 25 and theknuckle N are integrated with each other, and hence it is possible torealize simplification (facilitation) of assembly work in vehicleassembly plants.

As described above, the backlash at the bonding portion between the hubwheel 1 and the constant velocity universal joint 3 can be suppressed,and the backlash between the outer member 25 and the knuckle N can beeliminated. Thus, it is possible to realize improvement of NVHcharacteristics of a vehicle using the bearing device for a wheel.

Next, FIGS. 18A and 18B illustrate a modification of the integralconnection structure 85. The integral connection structure 85 isconfigured by welding in FIG. 18A, and configured by caulking of theouter member 25 which omits the fixing member 86 in FIG. 18B. In otherwords, without performing the plastic working on the axial end portions86 a, 86 b of the fixing member 86 of FIG. 18A, the axial end portions86 a, 86 b and the end surfaces 90 a, 90 b of the knuckle N are bondedto each other by welding. In this case, the welded portion may be theentire or part of the circumference. In FIG. 18A, a reference symbol 91denotes the welded portion.

In FIG. 18B, the outer diameter dimension of the outer member 25 is setto substantially the same as the hole diameter of the fitting hole 92 ofthe boss section 90 of the knuckle N. Further, the outer member 25 isfitted in the boss section 90, and the axial end portions of the outermember 25 are caulked, whereby caulked portions 94, 94 are engaged withthe end surfaces 90 a, 90 b of the boss section 90 of the knuckle N.

As described above, the integral connection structure 85 may beconfigured by caulking or welding, is excellent in workability ofconnection, and can integrate the outer member 25 and the knuckle Nfirmly.

Incidentally, as illustrated in FIG. 19, on the inner surface 37 of thehole 22 of the hub wheel 1, there may be provided small recesses 95arranged at a predetermined pitch along the circumferential direction.The small recesses 95 need to have a volume smaller than that of therecesses 36. By providing the small recesses 95 as described above, itis possible to realize improvement of press-fit property of theprojections 35. That is, by providing the small recesses 95, it ispossible to decrease the volume of the extruded portion 45 formed duringpress-fitting of the projections 35, and to realize a reduction inpress-fit resistance. Further, the size of the extruded portion 45 canbe decreased, and hence it is possible to decrease the volume of thepocket section 50, and to realize improvement of processability of thepocket section 50 and strength of the shaft section 12. Note that, inFIG. 19, the small recesses 95 have a triangular shape with an acutetop. However, as illustrated in FIG. 20, the small recesses 95 may havea triangular shape with a round top. In addition, the small recesses ofvarious shapes such as a semi-elliptical shape and a rectangular shapecan be adopted, and the number of the small recesses can be arbitrarilyset.

In each of the embodiments, when the shaft section 12 of the outer race5 is inserted (press-fit) into the hub wheel 1, by heating a unit bodyincluding the hub wheel 1 and the roller bearing 2 mounted onto the hubwheel 1, the hole 22 (at least shaft section fitting hole 22 a) of thehub wheel 1 may be expanded in diameter. That is, the hole diameter ofthe hole 22 before heating is the value D as described above, and thehole diameter of the hole 22 after heating is the value D′ larger thanthe value D (see FIG. 3). In this case, the value D′ is set to besmaller than the value D1.

As described above, if the shaft section 12 is press-fitted into thehole 22 of the hub wheel 1, the hardness of the projections 35 is largerthan the hardness of the inner surface 37 of the hole 22 by 30 points ormore. Therefore, the projections 35 bite in the inner surface 37, andthe projections 35 form the recesses 36, in which the projections 35fit, along the axial direction.

In this case, the hole 22 is expanded in diameter by heating and allowsmovement in the axial direction of the projections 35. Then, bycanceling the heating state, the hole decreases in diameter to return tothe original diameter. In other words, the hub wheel 1 is thermallydeformed in the diameter direction when the projections arepress-fitted, and preload equivalent to this thermal deformation isapplied to a tooth surface of the projections 35 (surface of recessfitting regions). Therefore, it is possible to realize improvement ofadhesion property of the entire fitting contact regions 38 between theprojections 35 and the recesses 36, and the outer joint member and thehub wheel 1 are fastened firmly. Moreover, it is unnecessary to formspline sections and the like in a member (hub wheel 1, in this case) inwhich the recesses 36 are formed. The bearing device for a wheel isexcellent in productivity. Further, phase alignment of the splines isunnecessary. It is possible to realize improvement of assemblability,prevent damage to the tooth surfaces during press-fitting, and maintaina stable fitting state.

A heating expanding temperature is set to be lower than a guaranteedtemperature for components of the bearing device for a wheel. Here, theguaranteed temperature is a temperature at which there can be exertedfunctions of the components (sealing, grease, cage, encoder, and thelike) used in the bearing device for a wheel. If the heating expandingtemperature is lower than this temperature, the functions of thecomponents are not deteriorated.

As described above, the heating expanding temperature is set to be lowerthan the guaranteed temperature for components of the bearing device fora wheel, whereby the sealing, grease, and the like used in the bearingdevice for a wheel can exert their functions effectively, and it ispossible to guarantee the quality of the bearing device for a wheel.

It is sufficient that the hole 22 of the hub wheel 1 is expanded indiameter and heated within a range of the guaranteed temperature.Therefore, as a heating means for heating before press-fitting, therecan be used various heating means such as a furnace and a heater.

Incidentally, in each of the embodiments, the spline 41 constituting theprojections 35 is formed on the shaft section 12 side. Hardeningtreatment is performed on this spline 41 of the shaft section 12 and theinner surface of the hub wheel 1 is not hardened (raw material).Meanwhile, as illustrated in FIG. 21A according to a fifth embodiment, aspline 61 (including projected streaks 61 a and recessed streaks 61 b)subjected to hardening treatment may be formed on the inner surface ofthe hole 22 of the hub wheel 1, and hardening treatment may not beperformed on the shaft section 12. Note that, the spline 61 can also beformed by various machining methods such as broaching, cutting,pressing, and drawing, which are publicly known and used as conventionalmeans. Further, as the thermal hardening treatment, various kinds ofheat treatment such as induction hardening or carburizing can beadopted.

In this case, the projecting direction intermediate regions of theprojections 35 correspond to the position of the recess forming surface(outer surface of shaft section 12) before recess formation. That is,the diameter dimension (minimum diameter dimension of projections 35) D4of a circle connecting vertexes of the projections 35 as the projections61 a of the spline 61 is set to be smaller than an outer diameterdimension D6 of the shaft section 12. A diameter dimension (innerdiameter dimension of inner surface of fitting holes betweenprojections) D5 of a circle connecting bottoms of the recesses 61 b ofthe spline 61 is set to be larger than the outer diameter dimension D6of the shaft section 12. In other words, the dimensions are set in arelation of D4<D6<D5.

When the shaft section 12 is press-fitted into the hole 22 of the hubwheel 1, by the projections 35 on the hub wheel 1 side, the recesses 36,in which the projections 35 fit, can be formed in the outercircumferential surface of the shaft section 12. Thus, the entirefitting contact regions 38 between the projections 35 and the recessesthat fit on the projections 35 are brought into intimate contact witheach other.

That is, when the projections 35 of the recess-projection fittingstructure M are provided on the inner surface 37 of the hole 22 of thehub wheel 1, the projections 35 on the hub wheel 1 side bite in theouter surface of the shaft section 12, whereby the hole 22 of the hubwheel 1 is slightly expanded in diameter and allows movement in theaxial direction of the projections 35. If the movement in the axialdirection stops, the hole 22 decreases in diameter to return to theoriginal diameter. Thus, the entire regions of the fitting contactregions between the projections 35 and the recesses 36 of an oppositemember (outer surface of shaft), which fit on the projections 35, arebrought into intimate contact with each other.

Here, the fitting contact regions 38 are ranges 76 illustrated in FIG.21B and ranges from halfway sections to the tops of the ridges insection of the projections 35. Further, a gap 62 is formed on the outersurface side with respect to the outer circumferential surface of theshaft section 12 between the projections 35 adjacent to each other inthe circumferential direction.

As described above, when the projections 35 of the recess-projectionfitting structure M are provided on the inner surface 37 of the hole 22of the hub wheel 1, it is unnecessary to perform hardness treatment(heat treatment) on the shaft section 12 side. Therefore, the outer race5 of the constant velocity universal joint 3 is excellent inproductivity.

Even in this case, the extruded portion 45 is formed by press-fitting.Therefore, it is preferred to provide the pocket section 50 that storesthis extruded portion 45. The extruded portion 45 is formed on the mouthside of the shaft section 12, and hence the pocket section is providedon the hub wheel 1 side.

Note that, even in the bearing device for a wheel in which theprojections 35 of the recess-projection fitting structure M are formedon the hub wheel 1 side as described above, a shaft extended sectionhaving the outer diameter dimension for centering when beingpress-fitted to the hub wheel 1 may be provided at the end portion onthe opposite mouth side of the shaft section 12.

In the above description, the embodiments of the present invention aredescribed. However, the present invention is not limited to theembodiments and various modifications of the embodiments are possible.For example, the shape of the projections 35 of the recess-projectionfitting structure M is triangular in section in the embodimentillustrated in FIG. 2 and is trapezoidal in section in the embodimentillustrated in FIG. 4. Besides, projections of various shapes such as asemicircular shape, a semi-elliptical shape, and a rectangular shape canbe adopted. An area, the number, and a circumferential directionarranging pitch, and the like of the projections 35 can also bearbitrarily changed. In other words, it is unnecessary to form thespline 41 or 61 and form the projections (projected teeth) 41 a or 61 aof this spline 41 or 61 as the projections 35 of the recess-projectionfitting structure M. The projections 35 may be something like keys ormay form wavy mating surfaces of a curved line shape. In short, it issufficient that the projections 35 arranged along the axial directionare press-fitted into the opposite side, the recesses 36 adhering to andfitting on the projections 35 can be formed on the opposite side by theprojections 35, the entire fitting contact regions 38 of the projections35 and the recesses that fit on the projections 35 are brought intointimate contact with each other, and rotation torque can be transmittedbetween the hub wheel 1 and the constant velocity universal joint 3.

Further, the hole 22 of the hub wheel 1 may be a deformed-shape holesuch as a polygonal hole other than a circular hole. A sectional shapeof the end portion of the shaft section 12 fit and inserted into thishole 22 may be a deformed-shape section such as a polygon section otherthan a circular section. Moreover, when the shaft section 12 ispress-fitted into the hub wheel 1, it is sufficient that onlypress-fitting start end portions of the projections 35 have hardnesshigher than that of the regions where the recesses 36 are formed.Therefore, it is unnecessary to set the hardness of the entireprojections 35 high. In FIG. 2 and the like, the gap 40 is formed.However, the projections 35 may bite in the inner surface 37 of the hubwheel 1 up to the recesses among the projections 35. Note that, as ahardness difference between the projections 35 side and the side of therecess formation surface formed by the projections 35, as describedabove, it is preferred to set the hardness difference to be equal to orlarger than 30 points in HRC. As long as the projections 35 can bepress-fitted, the hardness difference may be smaller than 30 points.

The end surfaces (press-fitting start ends) of the projections 35 arethe surfaces orthogonal to the axial direction in the embodiments.However, the end surfaces may be surfaces tilting at a predeterminedangle with respect to the axial direction. In this case, the endsurfaces may tilt to the opposite projection side from the inner surfaceside to the outer surface side or may tilt to the projection side.

Further, in the embodiments, regarding the shape of the pocket section50, in its circumferential groove 51, the side surface 51 b on anopposite spline side is a tapered surface that expands in diameter fromthe groove bottom 51 c to the opposite spline side. However, the pocketsection 50 may not have the above-mentioned tapered surface. In short,the shape of the pocket section 50 only has to be a shape that can store(house) the extruded portion 45 to be caused. Therefore, a volume of thepocket section 50 only has to be capable of storing the extruded portion45 to be caused.

When the serrate portions 55 are provided, the serrate portions 55 areprovided in the axial end portion (on pocket section side) of the spline41 in FIG. 8. However, the serrate portions 55 may be provided on themouth section 11 side opposite thereto, in the axial intermediatesection of the spline 41, and in addition, over the entire axial lengthof the spline 41. Further, the number, the shape, and the like of theprojections (projected teeth) 55 a of each of the serrate portions 55can be arbitrarily changed. The serrate portions 55 may be provided onall projections 35 on the circumference, or may be provided on arbitraryprojections 35 of all the projections 35 on the circumference. Notethat, in the embodiments, the serrate portions 55 are provided on theprojections 41 a of the spline 41 constituting the projections 35.However, the serrate portions 55 may be provided in the recesses 41 b ofthe spline 41.

Note that, when press-fitting the projections 35, a member on which theprojections 35 are formed may be moved, with a member in which therecesses 36 are formed being stationary. Conversely, the member in whichthe recesses 36 are formed may be moved, with the member on which theprojections 35 are formed being stationary. Both of them may be moved.Further, as the rolling elements 30 of the roller bearing 2, rollers maybe used. In the constant velocity universal joint 3, the inner race 6and the shaft 10 may be integrated with each other through anintermediation of the recess-projection fitting structure M described ineach of the embodiments.

INDUSTRIAL APPLICABILITY

The present invention can be applied to bearing devices for a wheel ofthird generation having a structure in which one of inner racewaysurfaces of a double-row roller bearing is integrally formed with anouter circumference of a hub wheel integrally having a wheel attachmentflange, and fourth generation in which a constant velocity universaljoint is integrated with the hub wheel and the other inner racewaysurface of the double-row roller bearing is integrally formed with anouter circumference of an outer joint member constituting the constantvelocity universal joint.

REFERENCE SIGNS LIST

1 hub wheel

2 roller bearing

3 constant velocity universal joint

11 mouth section

12 shaft portion

22 hole

22 a shaft section fitting hole

24 inner race

31 caulked section

35 projection

36 recess

38 fitting contact region

45 extruded portion

50 pocket section

55 recess-projection portion (serrate portion)

H hardened layer

H1 hardened layer

M recess-projection fitting structure

The invention claimed is:
 1. A bearing device for a wheel, the bearingdevice comprising: a hub wheel; a constant velocity universal joint; anda double-row roller bearing comprising: an outer member having an innercircumference in which double-row outer raceway surfaces are formed; aninner member including the hub wheel having an outer circumference inwhich one of inner raceway surfaces opposed to the double-row outerraceway surfaces is provided, and an inner race externally fitted ontothe hub wheel and having an outer circumference in which another one ofthe inner raceway surfaces opposed to the double-row outer racewaysurfaces is formed; and balls accommodated in double rows between boththe raceway surfaces of the inner member and the outer member so as tofreely roll, the hub wheel, the double-row roller bearing, and theconstant velocity universal joint being unitized together, wherein arecess-projection fitting structure, in which the hub wheel and a shaftsection of an outer joint member of the constant velocity universaljoint are integrated with each other, is provided, the recess-projectionfitting structure being configured such that projections, which areprovided on one of an outer surface of the shaft section of the outerjoint member and an inner surface of a hole of the hub wheel so as toextend in an axial direction, are press-fitted to another one of theouter surface of the shaft section and the inner surface of the holealong the axial direction, and that recesses, which intimately fit onthe projections, are formed in the another one of the outer surface ofthe shaft section and the inner surface of the hole by the projections,and that entire regions of fitting contact regions between theprojections and the recesses are brought into intimate contact with eachother, wherein fitting between the inner race and a small diameter stepsection at an area corresponding to an outer surface side of therecess-projection fitting structure is non-interference fitting, and thefitting between the inner race and the small diameter step section atanother area is interference fitting, and wherein a circumferentialnotch section is formed in an inner surface of the inner race in thearea corresponding to the outer surface side of the recess-projectionfitting structure, whereby the non-interference fitting is realized. 2.A bearing device for a wheel according to claim 1, wherein thedouble-row roller bearing comprises the outer member having thedouble-row outer raceway surfaces at its inner circumference, the outermember being connected to a knuckle constituting a suspension devicethrough an intermediation of an integral connection structure.
 3. Abearing device for a wheel according to claim 2, wherein the integralconnection structure is configured by caulking at least one of theknuckle and the outer member.
 4. A bearing device for a wheel accordingto claim 2, wherein the integral connection structure is configured bycaulking a caulked member interposed between the knuckle and the outermember.
 5. A bearing device for a wheel according to claim 2, whereinthe integral connection structure is configured by welding the knuckleand the outer member together.
 6. A bearing device for a wheel accordingto claim 1, wherein the recess-projection fitting structure is realizedby press-fitting the shaft section of the outer joint member in a stateof heating and expanding in diameter the hole of the hub wheel, theentire regions of the fitting contact regions between the projections onthe outer surface of the shaft section of the outer joint member and therecesses, which fit on the projections, in the inner surface of the hubwheel are brought into intimate contact with each other.
 7. A bearingdevice for a wheel according to claim 6, wherein a heating expandingtemperature is set to be lower than a guaranteed temperature forcomponents of the bearing device for a wheel.
 8. A bearing device for awheel according to claim 1, wherein the recess-projection fittingstructure, in which the entire regions of the fitting contact regionsamong the projections on the outer surface of the shaft section of theouter joint member and the recesses, which fit on the projections, inthe inner surface of the hub wheel are brought into intimate contactwith each other, is realized by forming a tapered section for centering,which decreases in diameter along a press-fitting direction, to the holeof the hub wheel; press-fitting the shaft section of the outer jointmember into the hole of the hub wheel through an intermediation of thetapered section.
 9. A bearing device for a wheel, the bearing devicecomprising: a hub wheel; a constant velocity universal joint; and adouble-row roller bearing comprising: an outer member having an innercircumference in which double-row outer raceway surfaces are formed; aninner member including the hub wheel having an outer circumference inwhich one of inner raceway surfaces opposed to the double-row outerraceway surfaces is provided, and an inner race externally fitted ontothe hub wheel and having an outer circumference in which another one ofthe inner raceway surfaces opposed to the double-row outer racewaysurfaces is formed; and balls accommodated in double rows between boththe raceway surfaces of the inner member and the outer member so as tofreely roll, the hub wheel, the double-row roller bearing, and theconstant velocity universal joint being unitized together, wherein arecess-projection fitting structure, in which the hub wheel and a shaftsection of an outer joint member of the constant velocity universaljoint are integrated with each other, is provided, the recess-projectionfitting structure being configured such that projections, which areprovided on one of an outer surface of the shaft section of the outerjoint member and an inner surface of a hole of the hub wheel so as toextend in an axial direction, are press-fitted to another one of theouter surface of the shaft section and the inner surface of the holealong the axial direction, and that recesses, which intimately fit onthe projections, are formed in the another one of the outer surface ofthe shaft section and the inner surface of the hole by the projections,and that entire regions of fitting contact regions between theprojections and the recesses are brought into intimate contact with eachother, wherein fitting between the inner race and a small diameter stepsection at an area corresponding to an outer surface side of therecess-projection fitting structure is non-interference fitting, and thefitting between the inner race and the small diameter step section atanother area is interference fitting, and wherein a circumferentialnotch section is formed in an outer surface of the small diameter stepsection in the area corresponding to the outer surface side of therecess-projection fitting structure, whereby the non-interferencefitting is realized.
 10. A bearing device for a wheel according to claim1, wherein the projections of the recess-projection fitting structureare provided to the shaft section of the outer joint member of theconstant velocity universal joint, and the recesses, which intimatelyfit on the projections, are formed by the projections on the innersurface of the hole of the hub wheel by setting at least hardness ofaxial end portions of the projections to be higher than that of an innersurface portion of the hole of the hub wheel, and by press-fitting theshaft section into the hole of the hub wheel from a side of the axialend portions of the projections, whereby the recess-projection fittingstructure is realized.
 11. A bearing device for a wheel according toclaim 1, wherein the projections of the recess-projection fittingstructure are provided on the inner surface of the hole of the hubwheel, and the recesses, which intimately fit on the projections, areformed by the projections in the outer surface of the shaft section ofthe outer joint member by setting at least hardness of axial endportions of the projections to be higher than that of an outer surfaceportion of the shaft section of the outer joint member of the constantvelocity universal joint, and by press-fitting the projections on a sideof the hub wheel to the shaft section of the outer joint member from aside of the axial end portions of the projections, whereby therecess-projection fitting structure is realized.
 12. A bearing devicefor a wheel according to claim 1, wherein a pocket section that storesan extruded portion caused by formation of the recesses by thepress-fitting is provided on the shaft portion of the outer jointmember.
 13. A bearing device for a wheel according to claim 1, wherein apocket section that stores an extruded portion caused by formation ofthe recesses by the press-fitting is provided in the inner surface ofthe hole of the hub wheel.
 14. A bearing device for a wheel according toclaim 13, wherein the pocket section that stores the extruded portion isprovided on a press-fitting start end side of the projections of theshaft portion of the outer joint member, and wherein a collar sectionfor centering with the hole of the hub wheel is provided on an oppositeprojection section side in the axial direction of this pocket section.15. A bearing device for a wheel according to claim 1, wherein anyregions in a projecting direction of the projections of the shaftsection of the outer joint member correspond to a position of a recessforming surface before formation of the recesses of the hole of the hubwheel.
 16. A bearing device for a wheel according to claim 1, wherein aninner diameter dimension of the inner surface of the hole of the hubwheel is set to be smaller than a maximum diameter dimension of a circleconnecting vertexes of the projections of the shaft section of the outerjoint member, and to be larger than a maximum diameter dimension of therecesses in the outer surface of the shaft section among the projectionsof the shaft section of the outer joint member.
 17. A bearing device fora wheel according to claim 1, wherein a diameter dimension of an arcconnecting vertexes of the multiple projections of the hole of the hubwheel is set to be smaller than an outer diameter dimension of the shaftsection of the outer joint member, and an inner diameter dimension ofthe inner surface of the hole among the projections is set to be largerthan the outer diameter dimension of the shaft section of the outerjoint member.
 18. A bearing device for a wheel according to claim 1,wherein circumferential thicknesses of projecting direction intermediateregions of the projections are set to be smaller than circumferentialdimensions in positions corresponding to the intermediate regions inbetween the projections adjacent to one another in a circumferentialdirection.
 19. A bearing device for a wheel according to claim 1,wherein a sum of the circumferential thicknesses of the projectingdirection intermediate regions of the projections is set to be smallerthan a sum of circumferential thicknesses in positions corresponding tothe intermediate regions in the projections on an opposite side that fitin between the projections adjacent to one another in thecircumferential direction.
 20. A bearing device for a wheel according toclaim 1, wherein recess-projection portions are provided, along theaxial direction, to at least an axial part of a member provided withprojections.
 21. A bearing device for a wheel according to claim 1,wherein the recess-projection portions are provided, along the axialdirection, to at least the axial part of the member provided with theprojections, the recess-projection portions being formed into a serrateshape.
 22. A bearing device for a wheel according to claim 1, whereinthe outer joint member of the constant velocity universal jointcomprises a mouth section in which an inner joint member is mounted, andthe shaft section provided so as to project from a bottom portion of themouth section, and wherein, by caulking an end portion of the hub wheel,preload is applied to the roller bearing through an intermediation ofthe inner race of the roller bearing which is externally fitted onto thehub wheel, and the mouth section is out of contact with the end portionof the hub wheel.